This type of micronation is surrounded from all sides by another state (or at least on most sides -it can border the ocean). This means that any attempt at being accepted must take this 'mother country' into account, and will be most likely decided by it.

Economy

With civilization nearby, basic survival may be much more easier than in an isolated place (unless there is a blockade). It should be easier to find business partners, and earn money due to different legal standards between the countries.

Availability

Mostly started in abandoned or out of way locations, with unclear property rights. There are many such places, there may be entire neighborhoods or ghost towns available. The success will depend on more factors than that.

As an alternative for of independence, one could buy an entire town and become its owner and mayor.

Legal status

It is difficult to tear away a part of a state's territory, and declare it for one's own. Doing it inside of the state is still more difficult. At the least, one can expect legal challenges.

Examples

The Principality of Hutt River, an independent territory in Western Australia, founded in 1970 after a long-running dispute over wheat quotas.